Acid mine drainage treatment using pervious concrete and evaluation of chemical clogging impacts – column experiment

An investigation was conducted to evaluate hydraulic performance and chemical clogging of the concrete permeable reactive barrier (PRB) used to treat acid mine drainage (AMD). The pervious concrete PRB system is an emerging technology for AMD treatment. In the present study, pervious concrete mixtures were prepared at a 0.27 water/cementitious ratio using CEM I 52.5R cement with or without 30% fly ash and 9.5 mm granite aggregate. The AMD types used were obtained from a gold mine and from a coal mine. Porosity and permeability properties of the pervious concretes were measured before and after use to treat AMD. Subsequently, 2D slice image analyses were done using X-ray microcomputed tomography (microCT). It was found that the heavy metals comprising Al, Zn, Fe, Mn, Mg, Ni and Co, were removed at the high removal efficiency (RE) levels of 70–100%. Interestingly, critical reductions in porosity (P-crit) and permeability (K-crit) values were utmost at a short distance of 75 mm from the entrance, forming bottleneck clogging. Results showed that chemical clogging that ensued progressively during the experiment, adversely gave values of up to 30–40% reduction in RE values, up to 30–40% reduction in P-crit and 80–90% reduction in K-crit. MicroCT analysis of pore connectivity confirmed the occurrence of bottleneck clogging in the column reactors. Further studies are needed to investigate the long-term adverse impacts of chemical clogging that could potentially be employed to determine the PRB's longevity.